1. Field of the Invention
The present invention relates to a process for producing a flat coil for use in an electric motor, a deflecting coil, a transformer or the like and is specifically directed to a process for producing a flat coil by cutting up the rolled body of metal foil.
2. DESCRIPTION OF THE PRIOR ART
Conventionally, a coil of the wound type utilizing a copper wire wound in layers is employed as a coil for an electric motor or in the deflecting yoke of a cathode ray tube. As the size of the apparatus is reduced, the so called flat coils of very substantially reduced thickness have been developed and put into practical use. For example, a sheet coil can be produced by etching a sheet of copper foil laminated with an insulator sheet in a spiral pattern in a line having a width of 50 microns or so and used as a coil for a flat motor. Employing such a thin sheet coil significantly contributes to flattening and miniaturizing of motors.
While such a sheet coil is very effective for flattening appliances, the mass production of such sheet coils is difficult because it requires an etching technique of very high accuracy. Since such a special technique is necessitated, the coils cannot be produced readily by every manufacturer.
There has been a disclosure of a process wherein a web of copper foil to which an insulator film is applied is rolled up and cut into round slices in order to produce flat coils. However, such a process has not been put into practical use due to the problems of reliability and applicability to mass production. In particular, it is difficult to cut a rolled up sheet of copper foil into round slices of a predetermined axial length, that is, into flat coils of a predetermined thickness. Where, for example, a mechanical means or a laser beam is used for such cutting, there is a possibility that a burr may be produced on a cut face which causes short-circuiting of the coil produced. In order to eliminate such a shear drop on a cut face, the face must be polished smoothly. This step normally requires very much labor and much operating time. Accordingly, the use of the proposed disclosure is not well suited for mass production.
When it is attempted to produce flat coils by cutting a rolled up body of copper foil, conventional cutting methods are not employed in mass production since their capacity does not match their cost, because processing after cutting is difficult, and because too high an overall cost is required.
For example, investigation made by the inventors of the present invention has revealed that when a rolled up body of overlapping sheets of conductor foil with an insulating film is cut by electric discharge machining, particularly where a very thin conductor foil is used, there is the possibility that the strength of a portion of the conductor foil at an outer peripheral portion thereof may be insufficient so that a so called turnup may appear. This results in reducing the cutting speed. A portion of the conductor foil at the outer peripheral portion of the coil may also be cut so that the coil thus produced is defective. In the worst case, cutting itself may be impossible.
Further, a flat coil produced by this process still has drawbacks in that it is deformed as a result of the cutting and that the strength of the terminal portions is not sufficient.